|between this redirection and the command it should apply to.
< file.txt | grep foo
< file.txt grep foo # or more canonically: grep foo < file.txt
ShellCheck has found a stage in a pipeline that consists of a redirection but no command. This doesn't make sense because a redirection without a command will not read or write any data.
This is most likely to occur when deleting a command that had a redirection, but leaving a
| behind instead of moving the redirection to a different command:
# Match lines with line numbers nl < foo.txt | grep bar # Incorrect attempt at removing line numbers. grep now has no input: < foo.txt | grep bar # Line numbers correctly removed. grep now reads foo.txt as intended. grep bar < foo.txt
It's technically valid to do e.g.
echo foo | > "$(cat)" to truncate a file called "foo", but please consider rewriting such code.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.